Why is a zero score by a batsman called a duck?

The term is a shortening of “duck’s egg”, which was used long before cricket began. When referring to the Prince of Wales’ (the future Edward VII) score of naught on July 17, 1866, a contemporary newspaper wrote that the Prince “retired to the royal pavilion on a ‘duck’s egg'” because the shape of the number “0” is similar to that of a duck’s egg. The Concise Oxford Dictionary still cites “duck’s egg” as an alternative version of the term.